The invention relates to a circuit for the line synchronisation in a television receiver, comprising a frequency and/or phase controllable oscillator, with means for supplying a pulse-shaped line synchronisation signal and a pulse-shaped gate signal derived from the oscillator signal to a coincidence stage, an output terminal of which is connected to a phase discriminator for determining the phase difference between the synchronising signal and a reference signal which is also derived from the oscillator signal, furthermore comprising a low-pass filter for smoothing the output voltage of the phase discriminator, the oscillator being controllable by the smoothed voltage thus obtained.
In such a circuit an input signal is supplied to the phase discriminator only during part of the period. As known, this causes an increase of the pull-in range of the circuit while noise and disturbances which may occur in the remaining part of the period have no detrimental influence. It will be clear that an improvement with respect to noise and disturbances is obtained accordingly as the gate pulses are of shorter duration. This especially applies to the pulse-shaped disturbing signals which are caused by reflection, for example from mountains or from high buldings, of the high-frequency television signal and which may occur shortly after the useful line synchronisation signal. If, however, the gate pulses are of a very short duration compared with the duration of the line period, then the pull-in range is no longer increased as compared with the case that the phase discriminator can receive a signal during the entire period.